'Big Bang Theory' previews tonight's Leonard Nimoy cameo

How do you achieve nerd nirvana? Book Spock and the smartest guy on the planet for cameos.

The Big Bang Theory was already enjoying its most watched season to date (16.3 million) when it exceeded expectations by luring Leonard Nimoy and Stephen Hawking in the same week. “These are two fantasy gets,” Co-Creator/Executive Producer Bill Prady told EW. “Nimoy hits that level of pop culture fandom, and Stephen is the heir to Einstein. It’s a thrill beyond thrills.”

Since the men are heroes of Jim Parsons’ character, Sheldon, Parsons had the privilege of shooting scenes with both — though Nimoy participates only via voice-over as Sheldon’s conscience on tonight’s episode. (Hawking will appear on April 5). Nimoy had helped out the CBS comedy before: He actually provided an autographed napkin for a previous episode. This time, he spent an evening on the set with the cast and crew. Though Parsons was never a Star Trek viewer, Nimoy’s visit was a huge deal to Prady — though the scribe says he was “really restrained” around Spock’s alter-ego.

Here’s a sneak peek from tonight’s show:

Hosting high-profile guests now leaves the show in a bit of a pickle: How do they top Spock and Hawking? “George Lucas, maybe?” suggests Parsons. “Sheldon would want to give him a piece of his mind for certain episodes of Star Wars.”